Porphyria:

Not porphyrinogenic (NP)
No precautions needed.

Probably not porphyrinogenic (PNP)
No precautions needed.

Possibly porphyrinogenic (PSP)
Only used when no safer alternative is available.
Precautions motivated in vulnerable patients.

Probably porphyrinogenic (PRP)
Prescribed when no safer alternative is available.
Precautions motivated in all patients.

Porphyrinogenic (P)
Prescribed when no safer alternative is available.
Precautions must be taken in all patients.

Not yet classified (NC)
Safety not yet established and therefore should not be used. Prescribed only when no safer alternative is available. Seek advice from a porphyria specialist.